Air dry moisture content (2A1)

This method is required to adjust soil chemical results based on air-dry samples to an oven-dry (105oC)basis. When the air-dry moisture content (M%) is known, the correction from air-dryto oven-dry is as follows:

Bicarbonate Extractable Phosphorus - Colwell (9B2)

This popular Australian P test on milled air-dry sample is suitable for acidic, neutral and alkaline soils. The extractant is freshly prepared 0.5M sodium bicarbonate @ pH 8.5. The wide soil/extractant ratio of 1:100 and an extended shaking time of 16 h favours readily available and more slowly available forms of soil P, while suppressing the solubility of basic calcium phosphates often found in neutral and alkaline soils.

Electrical conductivity (EC) of 1:5 soil/water extract (3A1)

This test on milled air-dry sample at a soil/water ratio of 1:5 for 1 his suitable for use on all soils, irrespective of whether acidic or alkaline. It usually underestimates the soluble salt status of soils containing natural or added gypsum, particularly if ³ 1% of gypsum is present. Such soils would have an EC of about 2 dS/m. Soil EC x 0.336 (Method 3B1) approximates percent total soluble salts, while approximate soil ionic strength (Method 3C1) at 0.1 bar (I0.1) can be calculated as follows: I0.1= [0.0446*EC1:5 – 0.000173], where I0.1 has units of mM, and EC1:5 has units of dS/m @ 25oC.

Exchangeable Acidity (15G1)

Exchangeable Bases - Ammonium Acetate (15D3)

Exchangeable bases - 1M ammonium acetate at pH 7.0.

This rapid method for exchangeable cations in non-saline acidic through to slightly alkaline soils has no pre-treatment for soluble salts. It should yield similar data to those of method 15A1, except it can overestimate exchangeable Ca in soils containing calcium carbonate.

KCl-ext.S (10D1)

CaCl2 extractable B - ICP (12C2)

The soil is extracted with boiling 0.01M Cacl2 solution at a 1:2 soil:solution ratio for 10 mins. It is then quickly filtered to avoid any re-fixation of the solubilised B. The extract is then analysed by ICP-AES.

Mehlich3 ICP (18F1)

Water soluble nitrate - automated colour (7B1)

This method uses the same 1:5 soil/water suspension described for method 3A1. The filtered or centrifuged aliquot is subjected to automated colorimetric analysis based on the Griess-Ilosvay reaction, either by continuous segmented flow analysis (sub-method 7B1a) or by flow injection analysis (sub-method 7B1b) The methods specify reporting nitrate-N (mg N/kg) on an air-dry basis. Note that in some highly weathered soils with a measurable anion exchange capacity, water may not extract all of the adsorbed nitrate-N.

This index of soil P sorption embraces adsorption as well as precipitation reactions. In addition, it utilises the Colwell-P test on the same soil sample as a measure of current soil P fertility (PBI+ColP). Equilibrium soil extracts are obtained by shaking milled air-dry soil continuously for 17 h at a ratio of 1:10 (w/v) with a P equilibrating solution initially containing the equivalent of 1000 mg P/kg in 0.01M CaCl2. In method 9I2a, orthophosphate-P in final particulate-free supernatant solutions is analysed by a molybdenum-blue analytical finish, at a preferred absorbance of 882 nm. Methods 9I2b and 9I2c code for analytical finishes based on ICPAES and a vanadate-P colour finish, respectively. PBI+ColP is calculated as {[Ps (mg P/kg) + Colwell-P (mg/kg)] / c (mg P/L)0.41}, where Ps = freshly sorbed P and c = final solution P concentration. The methods specify reporting results on an air-dry basis.

pH: 1:5 SOIL:0.01M CaCL2 Suspension (4B2)

This pH test on milled air-dry sample is suitable for use on all soils, irrespective of whether acidic or alkaline. Values are usually unaffected by fertilisation prior to sampling, as changes to the soil’s ionic strength is masked by the calcium chloride. Code 4B1 indicates direct use of 0.01M CaCl2, at a soil/solution ratio of 1:5, with mechanical shaking for 1 h prior to pH measurement using calibrated electrodes positioned in the unstirred supernatant after settling of the suspension. Code 4B2 provides a similar measurement outcome but relies on the addition of 0.21M CaCl2 to a 1:5 soil/water suspension to achieve 0.01M CaCl2 prior to measurement of pH as for 4B1.

Codes 4B3 and 4B4 are identical to 4B1 and 4B2, respectively, except the soil/CaCl2 suspensions are stirred during measurement. Method 4B5 codes for an MIR surrogate measurement. There is merit in separate use of both water and calcium chloride to measure soil pH.

pH of 1:5 soil/water suspension (4A1)

This test on milled air-dry sample involves mechanical shaking with deionised water in a closed system for 1 h at a soil/water ratio of 1:5 prior to pH measurement using calibrated electrodes, while stirring the soil/water suspension. The method is suitable for use on all soils, irrespective of whether acidic or alkaline. Values may be lower than expected on recently fertilised soils due to a temporary increase in soil solution ionic strength.

Chloride - 1:5 soil/water extract (5A2)

Tests for water-soluble chloride (Cl) on milled air-dry sample are suitable for use on all soils. For method 5A1, Clâ€‘in clarified 1:5 soil/water extracts is determined by potentiometric titration with AgNO3 in conjunction with an Ag/AgNO3 electrode array. For method 5A2a, Clâ€‘in clarified 1:5 soil/water extracts is determined by an automated, continuous flow colorimetric procedure based on the formation — in the presence of ferric ions and free thiocyanate ions — of highly coloured ferric thiocyanate in proportion to the Clâ€‘ concentration.

Total soil N â€“ Dumas high-temperature combustion (7A5)

This method utilises automated and/or microprocessor controlled instrumentation, which mostly is able to measure at least total C, N and S in the same sample. Dumas-N dry oxidation includes all forms of soil N, without the need for lengthy pre-treatments, although results can occasionally differ from those expected in soils with high levels of fixed ammonium-N (lower results) and when soils are organically rich (high results, due to incomplete combustion resulting in the formation of methane rather than CO2). Typically, dry, finely-ground sample is subjected to high-temperature combustion (e.g. 950–1,250oC) in a stream of purified O2. An aliquot of the gases produced by combustion is carried by helium gas to a thermal conductivity cell for measurement of any N2 generated, a process typically taking 3–5 min. A heated copper catalyst reduces NOx to N2. The method specifies reporting results as %N on an oven-dry (105oC) basis.